A pressurized-water coolant nuclear reactor power plant typically has a reactor pressure vessel positioned in a pit formed by a thick-walled biological shield made of concrete which is heat resistant and of great structural strength. The shield is itself radially enclosed by a cylindrical concrete wall of large enough diameter to provide an annular space in which one or more steam generators are positioned and which are connected with the pressure vessel by coolant pipe lines which extend through the biological shield. One of more coolant pumps are also located in this annular space and interposed in the coolant pipe lines to provide for forced coolant circulation. The entire installation is enclosed by a spherical steel containment enclosure required to positively prevent escape of potentially dangerous fluids to the outer atmosphere.
Every precaution must be taken to prevent this containment enclosure from being punctured or otherwise damaged in the event the components outside of the biological shield should fail and with explosive force produce projectiles from broken pieces of metal. The cylindrical concrete wall which surrounds these components does not have the thickness and structural strength of the biological shield and, therefore, does not provide the maximum possible security against damage to the containment enclosure. If this enclosure is punctured, the coolant released by the failure escapes to the atmosphere.
A pressurized-water coolant reactor steam generator, and some other types, externally is a tall cylindrical shape possibly changing in diameter but remaining a substantially cylindrical construction. The coolant pipe lines are, of course, cylindrical. Only the coolant pump has a shape other than cylindrical. All of these parts are made of metal, normally steel, and they are highly stressed thermally and operate under the internal pressure of the water coolant which must be kept under a pressure high enough to keep it in its liquid phase.
An obvious solution to the problem of providing the greater security that is so plainly desirable might appear to be to enclose the components by concrete constructions massive enough to provide effective mechanical shielding for the steel containment enclosure. However, such a solution involves great cost and does not in any event provide vertical protection unless a completely closed roof is provided.
The object of the present invention is to provide greater security against such possible damage to the containment enclosure, without involving the great expense, and impracticality, of the above kind of solution.